The present application is directed to an implant for spacing apart vertebral members and, more particularly, to an implant configured to be positioned between the C1-C2 articular joint.
The spine is divided into four regions comprising the cervical, thoracic, lumbar, and sacrococcygeal regions. The cervical region includes the top seven vertebral members of the spine identified as C1-C7. The thoracic region includes the next twelve vertebral members identified as T1-T12. The lumbar region includes five vertebral members L1-L5. The sacrococcygeal region includes nine fused vertebral members that form the sacrum and the coccyx. The vertebral members of the spine are aligned in a curved configuration that includes a cervical curve, thoracic curve, and lumbosacral curve. Intervertebral discs are positioned between the vertebral members and permit flexion, flange, lateral bending, and rotation.
The cervical region is further divided into an upper cervical region that includes the C1 and C2 vertebral members, and the lower cervical region that includes the C3-C7 vertebral members. The C1 vertebral member includes a bony ring with wide lateral masses that extend to each side and have large, inferior surfaces that articulate with the C2 vertebral member. The C2 vertebral member includes lateral masses each with a superior articular facet that form a pair of articular joints with the C1 lateral masses. The C2 vertebral member acts as a pivot point for the C1 vertebral member with the primary range of movement between the vertebral members being rotational.
Atlantoaxial subluxation is the misalignment of the C1 and C2 vertebral members and may occur from a variety of conditions, such as major trauma, or a degenerative condition such as rheumatoid arthritis or osteoarthritis. Atlantoaxial subluxation may cause pain, headaches, or cervical spinal cord compression.
Fusion of the C1-C2 vertebral members is often prescribed to treat atlantoaxial subluxation. Fusion in this region of the spine is difficult because of the relative small working space requiring the fusion procedure to occur within the anatomic constraints of the patient. Previous fusion techniques have been difficult due to the placement of fasteners within one or both of the vertebral members. The difficulties may occur because of abnormalities in one or both vertebral members, or destruction of the articular joints due to bone loss at either vertebral member.